Influenza remains the most important epidemic infectious disease in the United States. Epidemics of influenza infections occur almost every year with severe morbidity and high excess mortality in the population. In recent years, the value of amandatine and rimantadine in the treatment or prevention of influenza A infections in normal persons has been demonstrated conclusively. However, the usefulness of these drugs for the treatment of severe influenza A infections or of influenza A infections in the high-risk population groups has not been documented. The purpose of this trial is to investigate the role of these drugs in that clinical setting. Accordingly, patients of all ages with chronic obstructive pulmonary disease (COPD), chronic heart disease, metabolic diseases such as diabetes, and normal patients 65 years of age or older, who acquired influenza A infections in the community will be entered into a double-blind, placebo-controlled study to determine if amantadine or rimantadine can be effective in reducing the duration these illnesses and preventing the severe sequelae which often follow influenza infections. The trial will also provide information on the natural course of disease in these patients. Finally, normal patients with severe influenza A infections will also be treated as part of this study.